Mechanisms to lift a vehicle axle are well known in the prior art. A brief survey of some of the prior art designs allows them to be categorized generally into two classes.
The first class is at least partially comprised of U.S. Pat. Nos. 6,871,862, 6,854,989, 6,311,993, 5,505,481, 5,018,756, 5,015,004 and 4,763,923 and U.S. Patent Application Publication No. 2004/0256820. Each generally shows an air bag connected at one end to the vehicle frame via a hanger bracket that is suspended below the frame. The other end of the air bag is connected to one end of a pivoting arm or arms. The other end of the pivoting arm is connected directly or indirectly to a vehicle axle. An identical arrangement to that just described is located on the other side of the vehicle frame. Generally speaking, inflation of the air bag causes the arm or arms to pivot and move rearwardly. The rearward movement pushes the axle upwardly. To lower the axle, the air bag is simply deflated.
U.S. Pat. Nos. 4,773,670 and 6,158,750 and European Patent Application Publication No. 04732 14A1 are part of the second class of prior art documents as they teach air bags which provide a lifting force that is perpendicular to the vehicle frame. Both U.S. Pat. Nos. 4,773,670 and 6,158,750 locate the air bag within a complicated parallelogram frame. The air bags act on the arms of the frame to directly or indirectly force the axle upwardly.
European Patent Application Publication No. 04732 14A1 differs from the above described patents of the second class in that it teaches air bags having one of end attached to the chassis and the other end attached a bridge between two frame members. The bridge is connected to an auxiliary frame. An air spring bellows is connected at one end to the auxiliary frame, thus locating it outboard from the air bags. The other end of the air spring bellows is connected to a platform. The axle is mounted to the platform.
The above-described prior art designs suffer from several disadvantages. For example, many of them require at least two air bags to move the axle. The air bags, their associated structures and control mechanisms add to the cost of the vehicle and take up valuable space on the underside of the vehicle. Further, many of the above-identified systems are complicated and thus making them unreliable and expensive to maintain and repair. In light of these disadvantages of the prior art, it would be desirable to have a lifting system for a vehicle axle that is simple and inexpensive.